1. Field of the Invention
This invention relates to a digital processing system for deriving a digitized error signal from a temporal stream of successive digitized input samples of an input signal, and then deriving a digitized synthesized signal corresponding to such input signal from the error signal. The input signal may represent a time-varying one-dimensional parameter, such as an audio signal by way of example. In such a case, all of the successive input samples define a parameter. Alternatively, the input signal may represent a collection of a plurality of separate time-multiplexed specified parameters, such as a television video signal, by way of example. In this latter case, each different spatially-located (i.e., having different horizontal and/or vertical spatial coordinates) pixel within an image frame may, by way of example, represent a separate parameter, so that successive level values of any individual one of the separate pixel parameters during each of successive image frames is defined by its own predetermined subset of digitized input samples of the input signal.
In any case, such a digital processing system includes a first loop which includes delay means for deriving the error signal from the input signal, and a second loop which includes delay means for deriving the synthesized signal from the error signal. Two respective examples of such a first loop is a digital pre-emphasis, finite impulse response (FIR) filter for a noise-reduced signal transmission system, and a digital differential pulse code modulator (DPCM) for a compressed-data signal transmission system. Two respective examples of the second loop are a de-emphasis infinite impulse response (IIR) filter for a noise-reduced signal transmission system, and an inverse DPCM for a compressed-data signal transmission system.
2. Description of the Prior Art
Digital processing systems, of the type described above, are known in the art. They employ an input signal comprised of a temporal stream of successive digitized input samples occurring at a given sample frequency. The level value defined by each of the input samples is represented by a multibit code comprised of N bits, where N is a given plural number capable of defining a maximum numerical value M. In the case of digitized television video zignal samples, by way of example, it is conventional to employ a multibit code comprised of eight bits, capable of defining all numerical (i.e., integral) values in a range extending from a minimum value of zero to a maximum value of 255. However, in the case of a television video signal, each derived error-signal sample (which defines a level value that is the difference between the respective level values of the current sample of the current image frame and a first given function of the corresponding sample of at least one previous image frame) is capable of having a level value in a range that extends from -255 to +255. Therefore, the dynamic range of a digitized error-signal sample is twice that of a digitized input-signal sample (thereby requiring one extra bit to represent both the polarity and absolute value of its algebraic level value).
Often, a digitized error signal comprised of (N+1)-bit samples, is derived at a transmitter and forwarded over a transmission channel to a receiver. At the receiver, a synthesized signal, comprised of N-bit samples, is derived from the received error-signal samples. The transmission in real time of (N+1)-bit samples at a given sample rate over a transmission channel requires a greater transmission-channel bandwidth than does the transmission of N-bit samples at the same given sample rate. Transmission-channel bandwidth is costly. Since both the input an synthesized signals are comprised of N-bit samples, the requirement that the transmission-channel bandwidth be wide enough to transmit (N+1)-bit samples is wasteful. In addition, the processing of (N+1)-bit samples requires more hardware than does the processing of N-bit samples. In the case of digitally-processed television video signals, which represent scanned images having both vertical and horizontal dimensions, the additional hardware required to process (N+1)-bit samples, rather than N-bit samples, can become quite significant.
The present invention overcomes the problem of the prior art by providing a technique for reducing the number of bits representing each error-signal sample from (N+1)-bits to N-bits, without the introduction of any irreversible loss in signal information.